Pistols turning brown

hi there,

anyone could give me a help as well?!
got a fruity pack going on, one plant each strain(banana, blackberry and mango kush).
They are all on week 6 of flowering
mango kush pistols are turning brown and curling already. Is this not too early for pistols be turning brown and curly already??

the 3 plants seems to be going well, apart from that buds dont seem to be fattening up too much.
Am I doing anything wrong?

Have a 400w led full spectrum, and another 2 70w leds full spectrum as well.
Having been feeding it using canna coco a+b
coco coir and perlite

thanks